Significant efforts have, and continue to be, devoted to providing environmentally acceptable disposal or recycling mechanisms for waste rubber articles, particularly crosslinked or vulcanized rubber such as that used in motor vehicle tires. This continuing need to provide an acceptable disposal/recycling route is particularly acute due to the sheer scale of production (e.g. it has been estimated that 37 million car and truck tires are being discarded annually in the UK and this number is set to increase, in line with the growth in road traffic and car ownership, by a further 39% by 2021) coupled with the fact that, as rubber tires are extremely durable, disposal via landfill is problematic because the rate of biodegradation is exceptionally slow. Consequently, implementation of EU legislation has banned the disposal of tires in landfill sites. Further, disposal by incineration carries environmental concerns as combustion of tires tends to release significant amounts of unburned hydrocarbons and noxious emissions into the atmosphere, and melting tires also produce large quantities of oil, which may cause contamination of soil and ground water. Therefore, there is an increasing need to identify alternative solutions that promote recycling of such rubber products ahead of disposal.
A number of potential recycling routes for rubber products have been suggested. For example, waste tires have been used as fuel in cement-making operations; as fillers (when finely ground) in new tires, outdoor athletics surfaces and road asphalt; or as mulch.
However, in order to account for the growing number of waste rubber products, alternative recycling routes must be found.
One of the largest potential recycling routes for waste rubber is in construction industry, but usage of waste tires in civil engineering is, to date, very low—only about 4.5% of used tires are currently recycled in civil engineering applications which tend to be small-scale applications in single projects. In particular, it is known to incorporate (blend) powdered rubber into dry mix cementitious formulations. For example, U.S. Pat. No. 5,244,304A discloses a paving composition that comprises a cement binder, a dispersible latex polymer binder, and a mineral aggregate filler. The filler may be made up of mineral fines such as fly ash, mineral aggregate such as sand, and/or an elastomeric filler such as ground rubber particles; U.S. Pat. No. 5,290,356 discloses a concrete/rubber product made from a mixture comprising Portland cement, rubber crumb, water and sand, aggregate or light aggregate; and KR-A-2011110967 discloses a tile adhesive comprising Portland cement, silica, ground tire rubber, methyl cellulose, cellulose fiber and a redispersible polymer powder (RDP) resin.
RDPs made from emulsion polymers, such as vinyl acetate/ethylene copolymers, styrene/butadiene copolymers, and vinyl acetate/versatic acid vinyl ester copolymers are widely used in various construction applications, such as cement-based tile adhesives (CBTA) and ETICS adhesives or reinforcement coats to improve the mechanical properties of the cementitious compositions.
It is an object of the present invention to provide a convenient and environmentally acceptable use for waste rubber products, in particular crosslinked or vulcanised rubber, e.g. ground tire rubber particles. It is an additional object of the present invention to provide modified RDPs which, when incorporated into hydraulically binding compositions such as cementitious compositions for example CBTAs or ETICS adhesives or reinforcement coats, provide an improvement in the adhesive strength of resultant hydraulically set composition.